Transmission control in two-way signal transmission systems



Jung 20,1944. KQH, AWS 2,352,081

TRANSMISS/ION CONTROL IN TWO-WAY SIGNAL TRANSMISSION SYSTEMS Fiied sept; 19, 1942- /NVE/vrof? K. H. DAV/S ATTOP/VFV Patented June 20, 1944 UNIT@ OFFICE A "rRANsMrss/ion c'oN'rRonIN Two-WAY o SIGNAL rritAlNSMISSION SYSTEMS Kingsbury H.v Davis,- Bernard'svillaN. J., assi-gnor -to'Bell Telephone Laboratories, Incorporated, 'New York,`N. Y., a corporation of New York Appiication's'ptembei 19, i942, Serial No. $8,974-

` '6 Claims.` (Cl.'178-4 4) The invention re1'ates'totwoway signal transmission` Systems, andparticuiarly to the `signalcontrolled switching circuits'used withsuch sys. tems to directionally 'control signal i. transmission therein while suppressing`- echoes and preventing singing. Y j T fz, v Such 'signal-controlled f 'switching circuits, commonly called echo Suppressors, usually em-g ploy two switching branches respe'ctii'fely 'cori'- nected to a different'one of the two oppositel'yv directed one-way signal transmission'paths at a terminal or intermediate point in a two-'way telephone system, leach' including arectifler for rectifying the portion of'. 'the 'signals diverted into the switching branch, and electromagnetic relays or other switchii'i'gdevicesn operated by the rectified signals tosuitably controlrthe transmission 'eiiiciencies oithesig'nal transmission paths .and to, effectively `disable the other ysvi/itch'-y ing' branch, 'so as `to provide 'the desired direc# tional 4control of signal transmission' while` suppressing echoes and preventing singing.

The 'copending patent application of K. HQ Davis and vA'. C.' Norwine Serial No. 421,704', iled December '5, 1941, which 'issued 'as Patent' 'NoQ operate in opposition on a differential circuit, which may be a differential relay, the differential circuit ,being unbalanced in one 'direction orthe other ldepending on which echo suppressor l branch is supplied with the 'stronger signal energy',tto so control the relative transmission efficiencies of the oppositel'y directed signal transmission paths as to give directional control o'f'the system with suppression of the echoesv of his'ls'peech' signals to the louder of the two talkers. "Ordinarily, the "latter sort of break-in,

2,306,689 on December' v'29,' 1942,' discloses such an echo'suppressor applied toa four-wireftelephone circuit with an' associated break-'in'y control circuitof theai'nplitude'type, which enables one subscriber by talking loudly to break in on another who is talking andh'as obtainedv directional control of the system, 'whilefthe latter continues to talk and regardless fof how'loudl'y' he is talking. This is 'accomplished' by the use" .of relatively insensitive auxiliary break-in'con trols properly located with respect'to the echo suppressor controls,'operating on' an'amplitude basis to disable the 'echo suppressor controls of the talking party when the'breaking" Apa'rty talks with Ythe required loudness. Such 'break-inoon-` trols necessarily have to be relatively lov'vy in s'ensitivity to avoid false operation by 'echoes of loud speech, which requires" that the breaking party talk substantially'jlouder 'than E.the talker who has controlin'orderto breakin."

In tests of echo Suppressors "onl'actual -tollci'rcuits, it has' appeared that it" would beadvantageous to permit break-,in'byatalke'r .who'was relatively weak but louder'than'th`e` otl`1er .talker on the'circuit. One Vknown arrangement {for' accomplishing this is the SO-,Cfall'ed','diierelntial'4 echo suppressor in'.` which f. tw'o` voiceoperated echo suppressor branches` respectivelycontrolled: fromv a different 'one of the .oppositely directed .,rtelephfne circuit,

which may be called diiierential break-in, is relatively slower "than amplitude break-in because the breaking party cannot get control of the system until after the'expiration of the hang-over in the echo suppressor branch controlled by the rst talker; that is, a talker` to take controlmust maintain his speech energy higher in amplitude than that of the party he is interrupting for a period at least as long as the hang-over in' operation of the echo suppressor branch controlled by the` latter, provided to prevent `signal clipping;

An object of the invention is 'to'improve the operation of break-'in echo Suppressors of the above-described types.v This is accomplished by combining differential and amplitude break-in controls in the same echo suppressor'insuch manner as to obtain the advantages 'of both. This is, the two types of break-in are combined so that the stronger of two Weak 'talkers can obtain control, whichl could lnot be done with vonly amplitude break-in, and also so that atalker who is' loud, can interrupt another talker no matter how loudly vthe latter is speaking, which could' not be done with only vdifferential break-in. Y V

The various objects and features of the invention will be better understood fromthe following detailed description when 'read in conjunction withjthe accompanying drawing' 'in'which the Single figure `shows'schematically an echo suppressor 'embodying the invention'applied to a four-wire telephone circuit.

In Fig; 1, the ,four-wire telephone circuit in-y cludes a' one-Way, two-Wire transmission path EA rincluding thev one-way amplifiers AE, normally conditioned to transmit inithe direction from' westv to 'east b'etweer'iv the west two-way line WLand 'the east two-way line EL, and a one-way,v two-wire transmission .path WA including the one-vs'l'ayY a-mplifieijsAw, normally conditioned to transmit in thedirection from east `to west between V the ,same two-way lines. The 'input of. the transmission pathfEA and the output of the transmission path WA are coupled at the west terminal of the four-wire telephone circuit in conjugate relation with each other and in energy transmitting relation with the twoway line WL by the hybrid coil Hw and associated line balancing network Nw, and the output of the transmission path EA and the input of the transmission path WA are coupled at the east terminal of the four-wire telephone circuit in conjugate relation with each other and inv energy transmitting relation with the two-way line EL by the hybrid coil HE and associated line balancing network NE.

Connected across the transmission path EA at an intermediate point I is the input of the west switching branch 2 of a differential echo suppressor, including the amplier-rectier 3 and one winding 4 of the differential relay DR, poled so that when it is energized by the rectified signals in the output of amplier-rectier 3 it tends to operate the relay DR to its upper contact. Similarly, connected acrOss the transmission path WA at an intermediate point 5 is the input of the east switching branch 6 of the difierential -echo suppressor, including the amplifierrectifier 'I and a second winding 8 of the diierential relay DR, wound in opposition to the winding 4', whichV when energized by rectified signals in the output of the amplier-rectifler 'I tends to operate the relay DR to its lower contact. As will be described in detail later in connection with the complete description of operation of the circuit of the drawing, the operation of the differential relay DR to its upper contact will cause the operation of switching relays to respectively connect a short-circuiting connection across the path WA at a point 9 beyond the point 5 to which the input of the west echo suppressor branch 6 is connected, and to disable the switching relays controlled by operation of the diiierential relayDR to its lower contact; and the operation of the differential relay to its lower contact will cause the operation of switching relays to respectively close a shoirt-circuiting connection across the path EA at a point I beyond the point I to which the west echo suppressor branch 2 is connected, and todisable the switching relays controlled by the `operation of the dilerential relay DR. to its upper contact.

Connected across the transmission path EA at a point II in front of the disabling point I0 is the inputl of a third switching control circuit I2 including the amplifier-rectier I3 and the electromagnetic relay I4 which when completely energized by operation of the amplifier-detector I 3 operates to put a breakin the short-circuiting connection across the path EAl at the point I0. Similarly, connected across the path WA at a point I5 in front of the disabling point 9 is the input of a fourth switching circuit I6 including the amplifier rectifier I'I and the relay I8 which when completely energized by operation of the amplier-rectier Il operates to put a break in thev short-circuiting connection across the path WA at the point 9. AsA indicated by the series resistances I9 in the input of the amplifier-rectifier I3, the switching circuit I2 is relatively insensitive compared to the echo suppressor switching branch 2, and, as indicated by the series resistances in the input of the amplifierrectifier II, the switching circuit I6 is relatively insensitive compared with the east echo suppressor branch 6.

In the subsequent description, it will be convenient to speak of a loud talker meaning one who can operate a break-in control, and a "weak" talker, meaning one who cannot. Since We are to deal with circuits from the terminals of which portions of signals are returned as echoes, it is assumed that a loud talker, in order to break in, must operate a control at least insensitive enough so that it will Iiotfoperate on the echo of the otherztalkers speech energy. The resistances I9 in the input of the amplifier-rectifier I3 in control circuit I2, and the resistances 20 in the input of the amplier-rectier I1 in control circuit I6, respectively, are therefore each selected to provide suiicient desensitization of the control circuits I2 and I6 to prevent their operation on the maximum amount of signal echo i which may be applied thereto from the associated signal transmission path in response to direct signal transmission in the oppositely directed transmission path.

Let it be assumed that a west telephone subscriber associated with ythe line WL starts to speak, and at that time the east subscriber associated with the line EL is silent. The speech waves of the'west subscriber received over the line WL will be impressed by the hybrid coil Hw on the path EAand will pass over that path with an amplification depending on the gain setting of the amplifiers AE to the hybrid coil HE. The main portion of these speech waves will pass through the hybrid coil HE to the line EL over which it will be transmitted tothe east subscriber, and another portion, due to imperfect balance of the line EL by the balancing network NE, willv be reilected into the input of the path WA and will pass as echoes over that path in the direction from east to west.

A portion of Wests speech Waves will be diverted at the point II in the path EA into the input of the controlcircuit I2, but, if the west subscriber is talking'with normal loudness, will be of insufficient amplitude level to overcome the desensitization of that control circuit produced by the resistances I9, and, therefore, will not operate the switching relay 4 in the output of the amplier-recter I3. n

Another portion of Wests speech waves will be diverted at the point I in path EA into the west echo suppressor switching branch 2 and will be amplied and rectified by the amplier-rectier'3. 'I'he rectified waves in the output of the amplier-rectifier 3 will be supplied as energizing current to winding'll of the differential relay DR and-the opposing winding 8 of that relay being unenergized `injvthe absence of a rectified signal output from the amplier-rectierfl with the east subscriber'silent, will cause the operation of that relay to its upper contact. This will cause switching relays Ri and R2 to be energized by current from the battery 2I over a circuit extending from' the positive terminal 'of that battery through the windings of relays Rz and R1, resistances 22, 23, thel normally closed contacts of switching relay R4, the closed upper contact and armature of relayiDR, and ground back to the negative terminal ofjbattery 2|, causing the operation of relays Ri andlRz. Also, when relay DRoperates toits upper'cori'tact, the condenser 24 normally charged vby battery 2| through the windings vof 'relays'R andRi and lresistance 22, will be dischargedto ground. The operation of the relay Riwill' 'close ashort-circuiting connection across the path WA at the point 9 eEectively disabling that path so. asto suppressthe echoes ofWests signals when'kthey arrive Vat that point inthe path.V The operation ci. 'relay Ra will put a break in the connection between the lower contact'of the differential relay DRand the resistance 281m the energizing circuit for the relays R3; and R4 from battery 25, 'preventing subsequent operation of the latter relays when the relay DR is operated to its lower contact in response to loud speech from the east subscriber, and during the hang-over operatingv period of relays R1 and R2 when the energizing circuit for the latter relays is broken by the break of the upper contacts of relay DR. The west subscriber by operating the relays R1 and R2 has thus obtained directional control of the system with suppression of the echoes of his signals. Now, let it be assumed that while the west sub scriber is still talking, the east subscriber associated with the line EL `starts to talk. The latters speech waves will pass from the line EL through the hybrid coil H s into the transmission path WA and will pass over that path in the direction from east to west towards the west subscriber. A portion of Wests speech waves will be diverted at the point I5 into the control circuit I6 and another portion will bediverted at the point 5 into the east echo suppressor branch E. If East is a weak talker (as previouslyA defined), his speech currents will not cause operation of the relatively insensitive control circuit IB, but the portion of his speech currents diverted into the east echo suppressor :branch G will cause operation of the amplifier-detector 'I in that branchv to apply energizing currents to the winding 8 of the diierential relay DR. If Easts speech waves applied to the input of the east echo suppressor branch B are weaker than Wests speech waves applied to the input of the west ec-ho suppressor branch 2, the energizing current supplied to the winding 8 ofthe differential relay DR will not be strong enough to shift the armature of the relay DR from the upper to the lower contact. The stronger energizing currents applied to the winding Il will maintain the armature of the relay DR on its upper Contact so that the relays Rrand R2 will be maintained operated to hold the transmission path WA blocked at the point 9 and the energizing circuit for the relays R3 and R4 disabled. Thus West will maintain directional control of the system for such talking conditions.

However, if the east subscriber begins to more loudly than west so that the energizing currents supplied by him to the winding 8 of the differential relay DR are of greater amplitude than the energizing currents 'applied to the winding ll of that relay in response to Wests weaker speech waves, the diferential relay DR will be operated to its lower Contact. As soon as the armature of the relay DR leaves the upper Contact', the -energizing circuit for the winding of the relays R1 and R2 through the upper contact and armature of relay DR from the :battery 2l is broken, but the latter relays will be maintained in the operated condition for a hang-over interval determined by the time required for the condenser 24 to be charged up to the potential of battery 2I through the windings of these relays and resistance 22, and the path WA will be maintained blocked at the point 9 and the switching relays R3 and R4 will be maintained disabled for this hang-over interval. Thus, if East desires to reverse control of the diierential echo suppressor circuit he must maintain his speech energy higher in amplitude than that of West for a period at least as long as the suppressor hangover.

- However, East may immediately break Wests directional control of the system, if he (East) talks with sufcient loudness to overcome the desensitization of the amplitude break-in control circuitl provided lby resistance 20, regardless of how loudly West is talking. If East does so, his speech signals will cause the operation of the amplier-rectier I 'I of the break-in control I6 and thus the operation of the relay I8 in its output to put a break in the short-circuiting connection across the path WA at the pointv 9-` which has been previously closed by operation of the switching relay R1 in response to Westsprevious signals. The consequent enabling of the path WA at the point 9 will allow Easts speech signals to be transmitted out over the output of that path through the hybrid coil Hw and over the line WL to the west subscriber and to be heard by, the latter. As described above, the portion of Easts stronger speech signals diverted from the path WA at the point 5 into the switching branch 6 and causing the operation of the amplifierdetector 1 to supply stronger energizing current to the winding 8 of the differential relay DR, will be effective to cause the disablingof the path EA to give directional control of the echo suppressor to East with suppression of his echoes, only if the latter talks louder than West for a time interval at least as long as thewest suppressor hang-over. l

However, if at the time East talks loud enough to operate his break-in control circuit I6, West is Vtalkingstill louder, the energizing current supplied to the winding 4 of the relay DR will be greater than that supplied to the Winding 8 of that relay, and the armature of they relay DR will be maintained on its upper Contact to continue the operation of the relays R1 and R2.y The continued` operation of the relay R1, however, will not continue the disabling of the path WA at the point 9 because of theV operation of the relay I8 in the east break-in control circuit I6 in response to Easts loud speech to put a break in the short-circuiting connection across the path WA at the point 9. The continued operation of the relay R2 will maintain the energizing circuits for the switching relays R3 and R4 disabled. Then, as both of the paths EA and WA are unblocked, each subscriber will hear the other and echoes of his own speech signals. y

Wests loud speech signals will also cause the operation of his break-in control circuitl2, to put a break in the short-circuiting connection across EA at the point I0, but this will have no eiect on the operation because that connection is already in the disabled condition because of the unoperated condition of relay R3 with relay DR operated to its upper contact.

In a similar manner, when the east subscriber talks irst so that his speech currents Cause the operation of the relay DR to its lower contact, the switching relays Rs and R4 will` be operated to respectively connect a disabling short-circuit across the path EA at the point II) and to disable the switching relays R1 and R2, so as to give directional control of the circuit to East. Then, if West desires to break in, he needs only to talk loud enough toovercome the desensitization of his break-in control circuit I2 to operate the amplier-rectier I3 and thus the relay I4 to put a break in the short-circuiting connection across the path EA at the point I0, to enable that path and allow his signals (Wests) to be transmitted out over that path through the hybrid coil HE to the line EL leading to the east subscriber.

If- WestsV interruptingl speech waves are louder than Easts the operation of the differential relay DR will be reversed. If West then maintains the amplitude of his speech waves greater than that of Easts speech waves for a time at least as long as the hang-over time of the switching relays Ra and R4, West will be able to operate his relays Rr. and R2 to respectively connect ashort-circuit across the path WA atthe point 9, and to disable the energizing circuit for the relays Rs and R4, so as to seize directional control of the circuit away from East.

However, if East is talking louder' than West at the time that West has operated his break-in control circuit I2 to disable the short-circuiting connection across the path the differential relay DR will be maintained operated to itsV lower contact with the result that relays R3 and R4 will be maintained operated and the relays R1l and R2 disabled. Thus, both paths EA andA WA will be operative and both subscribers will hear each otherand echoes.

While the arrangements of the invention have been shown as embodying certain speciiic forms Which are deemed desirable, various modifications of these forms which are within the spirit and scope of the invention will be apparent to persons skilled in the art.

Whaty is claimed is:

1. In combination in a two-way telephone sys- Y tent, oppositely directed one-way' transmissicn paths for the voice signals transmitted in opposite directions, a voice-operated diierential echo suppressor controlledk from' the two paths, operating to allow transmission over the path supplied with theA stronger signals While effectively disabling the path supplied` with the weaker signals, an auxiliary voice-operated control device connected to each path in front of the disabling point therein responsive to the supply of voice signals thereto a given amoun-t stronger than normal signals to preventthat path fromA being disabled," or toelTec`tively"remo-ve' the' disability from that' pat-hiralreadyI disabled;

2-. The system of claim 1-, in which said differential echo suppressor comprises differential means, al voice-operated control branch connected tov each path operating to unbalance saiddifferential lmeans in one direction or the other depending on which control-branch is supplied with the greater amount of voice signal energy, and switching means responsive to the unbalance of said diierential meansin-one direction when the signals i-nonepathare stronger thanthe signals in;` the.v other path, to insertau disabling loss in saidother path, andi responsiveftolunbalahce of said differential means inthe other direction when the signals in-'sa'idotl'ierpath are stronger than` the signals in' said onel path, to' insert a disablinglossfin saidone path, andlsaid-a'uxiliary voice-operated control devicev connected toV each path is less sensitive thanv the echoI suppressor' control branch connected thereto by al given'l amountsuflicient to prevent false operation of the device by the I'naXinnimv amount f applied echoes of the signals" which may betransmitted over the other path', and when operated effectively prevents a disablingloss from ybeing inserted in the iirstl path, or effectively removes the loss therefrom when already inserted.

,3. Inatwo-way telephone system,- two oppositely directed ene-way transmission paths for respectively transmitting the oppositely directed voice signals of the' subscribers at opposite terminals of the system, a voice-operated differential echo suppressor controlled from the two paths, operating to allow transmission over the path supplied with the stronger signals and to eiective'ly disable the other path, so as to give directional control vof the system to the subscriber talking loudest and to suppress echoes of his' signals, and other switching means connected to each path in front of the disabling point therein, operating in response to voice signals in that path, only if at least a given amount stronger than normal signals, to prevent the disabling of that path orto reenable it if already disabled.

4. The system of claim 3', in which said dilerential echo suppressor has a given amount of hang-over in its operation to prevent signal clipping onv cessation of the supply of controlling signal energy, so as to prevent an interrupting subscriber from reversing directional control of said system unless he talks louder than the subscriber who has obtained control for a time interval at least asv long as the amount of echo suppressor hang-over.

5. The system of claim 3, in which said other switching means connected to each path is less sensitive than the differential echo suppressor by an amount at least sufcient to prevent false operation of the former by the echoes of the loudest voice signals transmitted over the other path.

6. In a two-Way telephone system including oppositely directed one-way paths for respectively transmitting the ysignals of the subscribers at opposite terminals of the system, a voice-operated echo suppressor having a given amount of hangover in its operation, operating to give directional control of the system to the one ofr two talking subscribers at opposite terminals of the system who talks loudest with suppression of the echoes of his signals, and to reverse directional control of the system obtained by one talker, in response to the voice signals .olf the other louder talker, only aterexpiration of' the suppressor hang-over applied' by the voicesignals of saidoh'e talker, and an auxiliary voice-operated switching control connected to each transmission path, respons'ive to the voice signals of a subscriber supplied to that path, only if such signals are a given amountstronger than normal voice signals, to interrupt directional control of the system obtained by the other `subscriber so as to enable voice signal transmission Ibetween the subscribers in bothdirections without suppression of signal KINGSBURY H. DAVIS. 

